feat: Drop Emacs 27.x #607

Job	Run time
test (ubuntu-latest, 28.2, false)	1m 7s
test (ubuntu-latest, 29.4, false)	1m 27s
test (ubuntu-latest, 30.1, false)	1m 4s
test (macos-latest, 28.2, false)	1m 46s
test (macos-latest, 29.4, false)	2m 2s
test (macos-latest, 30.1, false)	1m 58s
test (windows-latest, 28.2, false)	1m 32s
test (windows-latest, 29.4, false)	2m 55s
test (windows-latest, 30.1, false)	2m 41s
test (ubuntu-latest, snapshot, true)	52s
test (macos-latest, snapshot, true)	1m 45s
test (windows-latest, snapshot, true)	1m 49s
	20m 58s

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